TUESDAY, Dec. 10, 2013 (HealthDay News) -- People who take certain acid-reflux medications might have an increased risk of vitamin B-12 deficiency, according to new research.

Taking proton pump inhibitors (PPIs) to ease the symptoms of excess stomach acid for more than two years was linked to a 65 percent increase in the risk of vitamin B-12 deficiency. Commonly used PPI brands include Prilosec, Nexium and Prevacid.

Researchers also found that using acid-suppressing drugs called histamine-2 receptor antagonists -- also known as H2 blockers -- for two years was associated with a 25 percent increase in the risk of B-12 deficiency. Common brands include Tagamet, Pepcid and Zantac.

"This study raises the question of whether or not people who are on long-term acid suppression need to be tested for vitamin B-12 deficiency," said study author Dr. Douglas Corley, a research scientist and gastroenterologist at Kaiser Permanente's division of research in Oakland, Calif.

Corley said, however, that these findings should be confirmed by another study. "It's hard to make a general clinical recommendation based on one study, even if it is a large study," he said.

Vitamin B-12 is an important nutrient that helps keep blood and nerve cells healthy, according to the U.S. Office of Dietary Supplements (ODS). It can be found naturally in meat, fish, poultry, eggs, milk and other dairy products. According to the ODS, between 1.5 percent and 15 percent of Americans are deficient in B-12.

Although most people get enough B-12 from their diet, some have trouble absorbing the vitamin efficiently. A deficiency of B-12 can cause tiredness, weakness, constipation and a loss of appetite. A more serious deficiency can cause balance problems, memory difficulties and nerve problems, such as numbness and tingling in the hands or feet.

Stomach acid is helpful in the absorption of B-12, Corley said, so it makes sense that taking medications that reduce the amount of stomach acid would decrease vitamin B-12 absorption.

More than 150 million prescriptions were written for PPIs in 2012, according to background information included in the study. Both types of medications also are available in lower doses over the counter.

Corley and his colleagues reviewed data on nearly 26,000 people who had been diagnosed with a vitamin B-12 deficiency and compared them to almost 185,000 people who didn't have a deficiency.

While 12 percent of people with a vitamin B-12 deficiency had taken PPIs for more than two years, 7.2 percent of those without a deficiency had taken the medications long-term.

Of those with a deficiency, 4.2 percent took an H2 blocker for two years or longer, while 3.2 percent of those without a deficiency took the drugs for two years or more.

The risk of developing a vitamin B-12 deficiency was 65 percent higher for the long-term PPI users and 25 percent higher for those taking H2 blockers, according to the study.

People who took higher doses were more likely to develop a vitamin B-12 deficiency. People who took an average of 1.5 PPI pills per day had almost double the risk of developing a deficiency compared to those who averaged 0.75 pills per day, the study found.

Women had a greater risk of deficiency than men, and people younger than 30 taking these medications had a greater risk of developing a deficiency than older people, according to the study.

The risk of vitamin B-12 deficiency decreases when you stop taking the medications, but doesn't disappear completely, Corley said.

The study's findings were published in the Dec. 11 issue of the Journal of the American Medical Association. Although the study found an association between taking acid-reflux drugs long-term and having a higher risk of a B-12 deficiency, it didn't establish a cause-and-effect relationship.

If you're taking acid-suppressing medications, Corley said, "our study doesn't recommend stopping those medications, but you should take them at the lowest effective dose." And people shouldn't start taking vitamin B-12 supplements on their own, but should discuss it with their doctor, he said.

One expert had concerns about how frequently acid-suppressing drugs are used.

"This study found an adverse effect associated with taking these drugs," said Victoria Richards, an associate professor of medical sciences at the Frank H. Netter M.D. School of Medicine at Quinnipiac University, in Hamden, Conn. "It's also concerning that these drugs are used at such a high rate. Why do so many people have the need to suppress acid so much?"

The bottom line, Richards said, is that if you are having any symptoms of vitamin B-12 deficiency and you've been taking these medications, talk to your doctor about whether you should be tested for a deficiency. Tell your doctor if you've been taking over-the-counter acid-suppressing medications, so your doctor can properly evaluate your risk.